Page 220 - The Miracle of the Blood and Heart

THE MIRACLE OF THE
BLOOD AND HEART

of the capillaries are exceedingly thin, and possess special
structures that permit small molecules to pass through them.
In short, such vital functions as nourishing the tissues and
providing them with oxygen, while collecting their wastes, all
take place thanks to these capillaries.
The capillary walls are 0.5 microns in thickness. In these
walls, there are a number of gates through which substances
are exchanged. All essential substances for the cells must pass
through these gates. However, some plasma proteins are too
large to be able to pass through. This means that only appro-
priate substances can cross into the tissues, and that other
molecules must stay in the blood and continue on their way.
At the same time, these proteins prevent blood plasma from

Blood cell Capillary

WHAT IS THE TRANSPORT
Diffusion of
MECHANISM OF CAPILLARIES? Interstitial molecules
fluid
a) An exchange of substances
between the blood and the tissue Tissue
cell
cells takes place by means of the
interstitial fluid. a)
b) This diagram shows the four dif-
ferent means of transport through Intercellular Endothelial Connective
cleft tissue
the endothelial cell wall. pore

Diffusion
through
Direct Diffusion Vesicles pore
diffusion through
intercellular
Harun cleft
Yahya b)

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